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Detailed feature-level description, Rf02, Rf power amplifier (pa) – Rainbow Electronics RF02 User Manual

Page 3: Crystal oscillator, Low battery voltage detector, Wake-up timer, Event handling

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RF02

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DETAILED FEATURE-LEVEL DESCRIPTION

The RF02 FSK transmitter is designed to cover the unlicensed frequency bands at 433, 868, and

915 MHz. The device facilitates compliance with FCC and ETSI requirements.

PLL

The programmable PLL synthesizer determines the operating frequency, while preserving accuracy

based on the on-chip crystal-controlled reference oscillator. The PLL’s high resolution allows the usage of

multiple channels in any of the bands. The FSK deviation is selectable (from 30 to 210 kHz with 30 kHz

increments) to accommodate various bandwidth, data rate and crystal tolerance requirements, and it is

also highly accurate due to the direct closed-loop modulation of the PLL. The transmitted digital data can

be sent asynchronously through the FSK pin or over the control interface using the appropriate

command.

RF Power Amplifier (PA)

The power amplifier has an open-collector differential output and can directly drive a loop antenna

with a programmable output power level. An automatic antenna tuning circuit is built in to avoid costly

trimming procedures and the so-called “hand effect.”

Crystal Oscillator

The chip has a single-pin crystal oscillator circuit, which provides a 10 MHz reference signal for the

PLL. To reduce external parts and simplify design, the crystal load capacitor is internal and

programmable. Guidelines for selecting the appropriate crystal can be found later in this datasheet.

The transmitters can supply the clock signal for the microcontroller, so accurate timing is possible

without the need for a second crystal. When the chip receives a Sleep Command from the microcontroller

and turns itself off, it provides several further clock pulses (“clock tail”) for the microcontroller to be able to

go to idle or sleep mode. The length of the clock tail is programmable.

Low Battery Voltage Detector

The low battery voltage detector circuit monitors the supply voltage and generates an interrupt if it

falls below a programmable threshold level.

Wake-Up Timer

The wake-up timer has very low current consumption (1.5 uA typical) and can be programmed from

1 ms to several days with an accuracy of ±5%.

It calibrates itself to the crystal oscillator at every startup, and then every 30 seconds. When the

oscillator is switched off, the calibration circuit switches on the crystal oscillator only long enough for a

quick calibration (a few milliseconds) to facilitate accurate wake-up timing.

Event Handling

In order to minimize current consumption, the device supports sleep mode. Active mode can be

initiated by several wake-up events: timeout of wake-up timer, detection of low supply voltage or through

the serial interface.

If any wake-up event occurs, the wake-up logic generates an interrupt, which can be used to wake